1. Field of the Invention
The present invention relates to a motor control method and apparatus for controlling a motor based on a pass timing signal indicating a timing in which a motor movable part or a member to be driven by the motor passes each of a plurality of preset defined positions.
2. Description of the Related Art
In a conventional sheet transfer mechanism of a printer, in general, a transfer roller for transferring a printing sheet is connected to a pulley attached to a rotation shaft of a motor via an endless belt, and is driven by a motor driving force which is transmitted via the endless belt. It is to be noted that a rotary encoder is usually attached to the transfer roller. This rotary encoder outputs two-phase (phases A, B) pulse string signals which are synchronized with the rotation of the transfer roller and which have a predetermined phase difference from each other. Moreover, a motor control apparatus for driving/controlling the motor detects rotation direction and angle of the transfer roller based on these two-phase pulse string signals, and rotates the transfer roller to a targeted rotation position.
Concretely, with the rotation of the transfer roller, the rising and falling edges of the pulse string signals of two phases correspond to timings in which slits formed at equal intervals along the outer edge of the disc-shaped slit plate of the rotary encoder pass one light emitting element and two light receiving elements in the photo interrupter of the rotary encoder. Therefore, in the motor control apparatus, when the predetermined edges in the pulse string signals of two phases are successively counted based on a phase relation between the pulse string signals of two phases, the rotation position of the transfer roller can relatively be detected.
Moreover, as shown in a timing chart of FIG. 11, the motor control apparatus stops the motor in the timing in which the edge corresponding to a target rotation position is detected, and stops the transfer roller in the target rotation position.
Additionally, various forces such as the tensile force of the endless belt act on the rotation shaft of the motor. Therefore, when the motor is stopped, the rotation shaft of the motor sometimes rotates in a reverse direction by these forces (this reverse rotation will be hereinafter referred to as xe2x80x9creturnxe2x80x9d). Moreover, in the motor control apparatus, the motor is stopped in the timing in which the target rotation position is reached. Therefore, even with the micro return amount of the transfer roller generated by the return of the motor, the photo interrupter of the rotary encoder detects the slit corresponding to the target rotation position again, which has already been detected. In this case, it is sometimes judged that the roller has returned by one slit.
Following this judgment, in order to stop the transfer roller in a correct position, the motor control apparatus supposedly assumes that the transfer roller has actually returned by one slit, rotates the transfer roller by one slit, and corrects the rotation position of the transfer roller. However, in actual, when the return amount of the transfer roller is micro and less than the amount corresponding to one slit, a printing position into the printing sheet deviates by the correction. This causes a problem that printing quality is deteriorated.
Moreover, when the motor control apparatus is set not to correct the rotation position of the transfer roller for the return by one slit in consideration of the above-described problem, the printing quality can be prevented from being deteriorated for the micro return. However, the actually generated return by one slit cannot be handled, and the printing quality is deteriorated.
That is, in the related art apparatus, it has been difficult to judge whether or not the correction is necessary for the return of the motor.
The present invention has been developed to solve the above-described problems, and an object thereof is to provide a motor control method and apparatus for preventing a motor movable part or a member to be driven by a motor from passing a target stop position again in a reverse direction even with a micro motor return.
To attain this and other objects. according to the present invention, there is provided a motor control method for controlling a motor based on a pass timing signal indicating a timing in which a motor movable part or a member to be driven by a motor passes each of a plurality of preset defined positions. On detecting the timing corresponding to a target stop position in which the movable part or the member to be driven is to be stopped based on the pass timing signal, the motor is stopped in a preset stop timing while the movable part or the member to be driven reaches the defined position disposed beyond and adjacent to the target stop position.
According to the motor control method, the motor movable part or the member to be driven is stopped between the target stop position and the defined position disposed beyond and adjacent to the target stop position. Therefore, the motor movable part or the member to be driven can be prevented from passing the target stop position again in a reverse direction even with a micro motor return.
It is to be noted that the pass timing signal indicates a signal whose signal level is reversed every pass timing in which the motor movable part or the member to be driven passes the defined position.
According to another aspect of the present invention, there is provided a motor control apparatus comprising: a pass timing generator for generating a pass timing signal indicating a timing in which a movable part of a motor or a member to be driven by the motor passes each of a plurality of preset defined positions; and a stop instructing portion for instructing the motor to stop the movable part or the member to be driven in the defined position disposed beyond and adjacent to a target stop position, when detecting the timing corresponding to the target stop position in which the movable part or the member to be driven is to be stopped based on the pass timing signal generated by the pass timing generator.
In the motor control apparatus of the present invention constituted as described above, the pass timing generator generates the pass timing signal indicating the timing in which the movable part of the motor or the member to be driven by the motor passes each of a plurality of preset defined positions. Moreover, on detecting the timing corresponding to the target stop position in which the movable part of the motor or the member to be driven is to be stopped based on the pass timing signal, the stop instructing portion instructs the motor to stop in the preset stop timing while the movable part or the member to be driven reaches the defined position disposed beyond and adjacent to the target stop position.
That is, the apparatus constituted as described above realizes the motor control method according to the present invention, and can obtain an effect similar to that of the method according to the present invention.
It is to be noted that for the stop timing, the stop instructing portion includes a timer for starting measurement of time, on detecting the timing corresponding to the target stop position, and a time at which the timer ends the measurement of a preset delay time may also be set to the stop timing.
Moreover, according to the present invention, the pass timing generator includes an encoder for generating a pulse string in which at least one of rising and falling edges corresponds to the pass timing of the defined position as the pass timing signal. In this case, the stop instructing portion may include: a delay edge detector for detecting the edge of the pulse string generated while the movable part or the member to be driven passes the defined position corresponding to the target stop position and reaches the defined position disposed beyond and adjacent to the target stop position; and a stop timing generator for generating the stop timing based on the timing of the edge detected by the delay edge detector.
In the stop instructing portion constituted in this manner, the delay edge detector detects the edge of the pulse string generated while the movable part of the motor or the member to be driven passes the defined position corresponding to the target stop position and subsequently reaches the defined position disposed beyond and adjacent to the target stop position. The stop timing generator generates the stop timing based on the timing of the edge detected by the delay edge detector.
That is, the motor is stopped in the stop timing generated based on the edge of the pulse string generated between the target stop position and the adjacent defined position. Therefore, the movable part of the motor or the member to be driven can be stopped between the target stop position and the defined position disposed beyond and adjacent to the target stop position.
It is to be noted that in the present invention when the encoder generates the pass timing signal as well as a direction judgment signal having a phase different from that of the pass timing signal, the delay edge detector may also be constituted to detect the edge of the direction judgment signal.
In this case, the stop timing generator can generate the stop timing based on the timing in which the delay edge detector detects the edge of the direction judgment signal.
That is, the stop timing of the movable part of the motor or the member to be driven can more finely be set.
Here, the stop timing generator may generate the timing of the edge detected by the delay edge detector as the stop timing. Alternatively, the stop timing generator includes the timer for starting the measurement of time by the timing of the edge detected by the delay edge detector, and may generate a time at which the timer ends the measurement of the preset delay time as the stop timing.
It is to be noted that according to the present invention the encoder may include a rotary or linear encoder, or may include an optical or magnetic encoder.